Synthesis and photophysical characterization of porphyrin and porphyrin–Ru(ii) polypyridyl chromophore–catalyst assemblies on mesoporous metal oxides

Abstract

A layer-by-layer procedure has been used to prepare chromophore–catalyst assemblies consisting of phosphonate-derivatized porphyrin chromophores and a phosphonate-derivatized Ru(II) water oxidation catalyst on the surfaces of SnO₂ and TiO₂ mesoporous, nanoparticle films. In the procedure, initial surface binding of the phosphonate-derivatized porphyrin is followed in sequence by reaction with ZrOCl₂ and then with the phosphonate-derivatized water oxidation catalyst [Ru^II(2,6-bis-(1-methylbenzimidazole-2-yl)pyridine)(2,2′-bipyridine-4,4′-hydroxymethylphosphonate)(H₂O)]²⁺, [Ru^II(Mebimpy)(4,4′-(PO(OH)₂–CH₂)₂-bpy)(OH₂)]²⁺. Fluorescence from both the free base and Zn(II) porphyrin derivatives on SnO₂ is quenched; substantial emission quenching of the Zn(II) porphyrin occurs on TiO₂. Transient absorption difference spectra provide direct evidence for appearance of the porphyrin radical cation on SnO₂via excited-state electron injection. For the chromophore–catalyst assembly on SnO₂, transient absorption difference spectra demonstrate rapid intra-assembly electron transfer oxidation of the catalyst following excitation and injection by the porphyrin chromophore.